Prior to the development of the present invention, as is generally well known in the art, a rotary door operator is mainly used in the inter-city bus coaches. These rotary operators are available in two distinct types, commonly referred to as zero-lead and lift-and-lock. Either door operator type can be adapted for use with pneumatic or hydraulic fluids.
Both rotary door operator types comprise a double acting cylinder typically attached to a flanged mounting bracket. The mounting bracket has an aperture for an output shaft which is attached at one end to the piston disposed with the double acting cylinder and coupled with a door post at a distal end. A cover is generally provided for encasing the double acting cylinder as well as any other rotary door operator components attached either to the double acting cylinder or to the mounting bracket.
In typical applications, the rotary door operator is mounted to the structure of the transit vehicle adjacent the portal aperture with the output shaft being vertically oriented in an upward direction in order to couple with the rotating door post. In such orientation and in such close proximity to the exterior surface of the transit vehicle, the rotary door operator is exposed to the environmental factors, such as dirt, dust, and especially moisture, when the door is opened to enable passenger ingress and egress of a particular concern is the aperture disposed within the mounting bracket which enables connection of the output shaft with the drive cylinder. Since the output shaft must be allowed to move both rotatably and axially, the aperture must be designed with sufficient clearance to enable such movement. However, such clearance also enables the environmental factors to infiltrate the interior portion of the door operator.
U.S. Pat. No. 4,813,293 to Fink teaches a cover arrangement for a rotary door operator which utilizes a cup-shaped seal fitting in an annular grove in the output shaft in combination the outwardly projecting collar disposed integrally within the output shaft and further disposed above such annular grove. The seal rests firmly against the surface of the mounting bracket adjacent the exposed end of the output shaft. Additionally, the opposite surface of the mounting bracket is provided with a perimeter seal for accepting the main cover member of such rotary door operator.
There are several disadvantages related to this type of design. In the first aspect, the outwardly projecting integral collar results in increased manufacturing costs of the output shaft which is generally machined either from a solid round stock or form the casting having additional material for machining allowance. In the second aspect, the perimeter groove in the mounting bracket requires a certain precision in cover manufacturing in order to achieve a predetermined fit. In the third aspect, the cup-shaped seal must be temporarily expanded during an assembly to fit over the collar and into the annular groove thus increasing the complexity of the assembly and disassembly process.
As it can be seen from the above discussion there is a need for a simplified approach to prevent infiltration of environmental factors into the interior portion of the rotary door operator.